Hyoseong Gwon

Anisotropic heat transfer characteristics of composite material enhanced with high thermal conductivity fiber

The target surface of divertor takes high heat flux from plasma in fusion reactor. Removal of heat generated on the surface of divertor is one of the most difficult problems that should be solved for realization of fusion reactor. Besides, high temperature heat transfer medium should be collected for the efficient utilization of energy. This study analyzed thermal conduction behavior of composite material for the application to the divertor target. Steady state analysis was conducted using finite element method. Fiber with circular cross section is arranged into matrix regularly or irregularly to express actually produced specimen. Mesh size of each model was 1μm, and directions of fiber to thermal conduction are 0, 45, 90 and degree, respectively. Uniform heat flux is applied to the top surface of each model, and temperature of the bottom surface in each model, is assumed to be controlled at 600°C, assuming a large capacity coolant at the stable temperature is fed to the surface. In the steady state, temperature on top surface of each model was measured 1μm apart. Thermal conductivity of each model was evaluated by average of the temperature. From results of analysis, calculated thermal conductivity of the composite was enhanced almost proportionally to volume fraction of fiber when heat flux and fiber are parallel. However, heat conduction was found to be affected by direction, distribution and arrangement of fiber. Heat conduction in the composite was found to be rather complicated and simple equation could not express it.

Evaluation of thermal conductivity of unidirectional SiC composite enhanced with carbon fibers

The authors have proposed a new divertor concept using SiC composite with directional high thermal conductivity enhanced with fiber as substrate of the divertor structure in fusion reactor. In this study, unidirectional SiC composite with pitch-based carbon fibers (UD-C_f/SiC) was fabricated as the model material. The thermal conductivity (or thermal diffusivity) in directions parallel (0°), inclined (45°), and transverse (90°) to the C_f orientation was measured by the laser flash method. The results were compared with monolithic SiC (mono-SiC) in order to evaluate the enhancement of thermal conductivity by an introduction of C_f. Although the thermal conductivity of the UD-C_f/SiC in directions of 45° and 90° was relatively lower than that of the mono-SiC, that of the UD-C_f/SiC in direction of 0° was ten times as large as that of the mono-SiC.